Activation of rac‐ethylenebis(indenyl)zirconium dichloride with a low amount of methylaluminoxane (MAO) for olefin polymerizations

Abstract

The homopolymerization of hex-1-ene catalyzed by the system rac-EtInd,ZrCI,/MAO was investigated in solvents of various polarity (toluene, methylene dichloride and heptane). Polymerization kinetics were monitored by dilatometry. It is shown that reaction proceeds by long-lived active species rapidly formed and remaining at constant concentration during the whole polymerization. However, the molar masses of the polymer remain controlled by a transfer process. A strong enhancement of the activity is observed in pure CH2C12 compared to the one measured in toluene. Besides, the use of CH,CI, allows to reduce the amount of methylaluminoxane (MAO) by a factor 20 to reach the plateau of maximum activity, without affecting the isotacticity of the polymer. The increase of activity in CH,CI,, even for low MAO/Zr ratios, is explained by an easier ionic dissociation of the Zr-X bond (X = C1 or methyl), yielding the formation of cation-like active species. A preformation of the catalytic system in minute amount of CH,Cl, followed by hex-1-ene polymerization in heptane or toluene was found to yield also high catalytic activity at a low MAO/Zr ratio. These results suggest that the beneficial effect of methylene dichloride on the formation of the active species is preserved. A tentative explanation is proposed. A first extension of the results obtained with the a-olefin to ethylene polymerization is also presented.

Reactivity of Metallocene Catalysts for Olefin Polymerization: Influence of Activator Nature and Structure

“…The same effect could be observed with toluene as the medium, when metallocene and MAO were pre-complexed in dichloromethane. [103] In metallocene catalysts, the key factor controlling the stereospecificity is the ligand framework around the tran- Table 3. Influence of the TMA content in MAO on ethylene/ styrene copolymerization with the system CpTi(OPh) 3 (Table 4).…”

Activation of iPr(CpFluo)ZrCl2 by methylaluminoxane, 3. Kinetic investigation of the syndiospecific hex-1-ene polymerization in hydrocarbon and chlorinated media

“…In a previous series of papers 13 -15) , related to a-olefin polymerization in the presence of the rac-Et(Ind) 2 ZrCl 2 /MAO catalytic system, we have shown the drastic effects of the polymerization media and polarity on the cationation process of the zirconocene by MAO and on the polymerization activity. Indeed, in methylene dichloride, it was possible to decrease by ten times the amount of MAO necessary to obtain complete activation of the metallocene 13) . Interestingly, no loss of isospecificity control was noticed in the hex-1-ene polymerization performed in the chlorinated solvent.…”

Effect of Ligand X in Cp*TiX3/MAO Catalysts on the Polymerization of Vinyl Chloride

“…Similar observations in the polymerizations of styrene and propylene in CH 2 Cl 2 where suggested to be due to a transition from metallocene/MAO contact pair in toluene to free and separated species in CH 2 Cl 2 , which leads to a decrease in the stereoregularity of the polymers. [13,14] The polymerization of VC with Cp*Ti(OR) 3 /MAO catalysts was not inhibited in the presence of free radical inhibitors, and the resulting polymers have no anomalous units due to a radical polymerization of VC. On the basis of these results, we suppose that the polymerization of VC with the Cp*Ti(OR) 3 /MAO catalyst systems proceeds via a nonradical mechanism.…”